1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus having the same, and more particularly relates to an image pickup apparatus using a solid-state image pickup element such as a video camera, an electronic still camera, a broadcasting camera, or a monitoring camera, or an image pickup apparatus using a silver salt film.
2. Description of the Related Art
An image pickup optical system used for an image pickup apparatus needs to be a zoom lens which has a short total lens length, a small size, a high zoom ratio, and a high resolution.
Commonly, in order to maintain a predetermined zoom ratio and also to reduce the size of a whole system, the refractive power of each lens unit constituting the zoom lens needs to be strengthened and also the number of the lenses needs to be reduced. However, in such a zoom lens, the thickness of the lens increases in order to ensure an edge thickness in accordance with the increase of the refractive power of each lens surface. In particular, a lens effective diameter increases and a whole of the lens system cannot be sufficiently shortened. At the same time, it is difficult to correct various kinds of aberrations such as a chromatic aberration at a telephoto end. Further, in accordance with the increase of the zoom ratio, an error which is caused by a tilt or a decentering in assembling a lens or a lens unit increases. When the sensitivity of the decentering of the lens or the lens unit is large, the optical performance is greatly deteriorated by the decentering or the optical performance is greatly deteriorated in an anti-shake operation. Therefore, it is preferable that the sensitivity of the decentering of each lens or each lens unit is reduced as much as possible.
A positive-lead type zoom lens which includes first, second, and third lens units having positive, negative, and positive refractive powers respectively, and a subsequent rear group including at least one lens unit in order from an object side to an image side is known. For example, a zoom lens which is constituted by four lens units having positive, negative, positive, and positive refractive powers in order from the object side to the image side is known (U.S. Pat. No. 7,190,529).
A zoom lens which is constituted by five lens units having positive, negative, positive, positive, and positive refractive powers in order from the object side to the image side is also known (U.S. Pat. No. 7,286,304).
Further, a zoom lens which is constituted by five lens units having positive, negative, positive, negative, and positive refractive powers in order from the object side to the image side is known (U.S. Pat. No. 6,594,087).
In these four-group zoom lens and five-group zoom lens, in order to realize a high zoom ratio and a reduction of the size of the whole lens system and also to obtain a good optical performance, it is important to appropriately set a refractive power or a lens configuration of each lens unit, a movement condition in a zoom operation of each lens unit, or the like. In particular, in order to reduce the lens effective diameter, to reduce the size of the whole of a camera, and also to well correct various kinds of aberrations such as a chromatic aberrations at the telephoto end, it is important to appropriately set the refractive power of the first lens unit, the movement condition of the first lens unit in the zoom operation, or the like. If these configurations are not appropriately set, it is difficult to reduce the size of the whole system and to obtain a zoom lens which has a wide field angle and a high zoom ratio and also has a high optical performance.